String, like in C, are not a built in type. They must be included with
a library.
#include <string>
std::string variable_name = "hello there";
Use the + opertor.
std::string message = "hello" + variable + ".";
Use the [].
std::string my_string = "hello there";
char letter = my_string[2];
std::string my_string = "hello there";
int string_length = my_string.length()